Peter Sutherland, the UN Secretary General’s special representative on international migration, said the British reaction to the crisis was “grossly excessive”.

The great majority of migrants heading to Europe are genuine refugees, he said, and Britain receives far fewer applications for sanctuary than other European countries.

He said calls to stop economic migrants entering the UK are "a xenophobic response to the issue of free movement".

He told the BBC: "In my opinion, the debate in the UK is grossly excessive in terms of Calais. We are talking here about a number of people – a relatively small number in the context of what other countries are having to do – who are in terrible conditions and have to be dealt with by France and/or Britain."

Thousands making the perilous boat voyage across the Mediterranean to reach southern Europe are "in the main" genuine refugees fleeing violence and persecution, he said.

Britain also receives far fewer asylum applications that other European countries, he said.

“Germany last year received 175,000 asylum applications. Britain received 24,000," said Mr Sutherland.

Migrants face police officers as they attempt to access the Channel Tunnel, in Calais (AP)

Mr Sutherland said: "I think it is most unfortunate to create an image of hordes of people, when in reality the highest figure I have seen for the actual numbers in the so-called 'jungle' around Calais – the place where these unfortunate people are living – is 10,000."

Kevin Hurley, police and crime commissioner for Surrey, earlier this week called for the 2nd Bn Royal Gurkha Rifles based just outside Hythe, Kent, to be deployed to make sure Britain’s border is secure.

French gendarmes try to stop migrants on the Eurotunnel site in Coquelles, near Calais (PHILIPPE HUGUEN/AFP)

Mr Sutherland said: “The first thing we have to do collectively is to deal with their conditions. Instead of talking about sending Gurkhas or building fences, we should be thinking of the humanitarian crisis."

Mr Sutherland urged the UK to join the common European approach to the migrant issue, warning: "Anybody who thinks that by erecting borders or fences in some way a particular state can be protected from alleged 'floods' – which are anything but floods – of migrants is living in cloud cuckoo land."